Rutile is a naturally occuring substantially pure TiO.sub.2, but ilmenite is the most wide spread and cheapest titanium-containing ore. Ilmenite is classically ferrous titanite, FeO.TiO.sub.2 or FeTiO.sub.3. In the natural state, the ilmenite is often associated with greater quantities of iron oxide and varying amounts of other impurities such as the oxides and sulphides of magnesium, aluminum, manganese and often trace amounts of vanadium and chromium. Silica is also a naturally occurring diluent of the ilmenite.
Commercially, ilmenite ores may be classified as high grade ores or low grade ores. The high grade ilmenite ores contain up to 50 wt % of TiO.sub.2 -equivalent and less than 30 wt % of total iron, as iron oxides. The low grade ilmenite ores generally have TiO.sub.2 -equivalent contents of less than 50 wt % and iron contents in excess of 30 wt % iron as the oxides. Some of the iron in the low grade ores, may be in the form of sulphides. The amount of other contaminating and diluting oxides is also greater in the low grade-ilmenite ores.
In the past, ilmenite has commercially been converted to TiO.sub.2 via the sulphate process. High grade ilmenites are dissolved in concentrated sulphuric acid and first hydrolyzed to titanium oxide hydrates and then these hydrates are calcined to the anatase form of TiO.sub.2. As anatase is the less preferred form of TiO.sub.2 for pigment production (its greatest commercial use) it must subsequently be transformed to the rutile form of TiO.sub.2.
It is desirable to obtain TiO.sub.2 directly in the rutile form. It is recognized in the industry that TiO.sub.2, in rutile form, is best obtained via the "chloride" process wherein titania from crude natural or synthetic rutile is chlorinated to form TiCl.sub.4 in pure form. The latter is then oxidized or burnt directly to form the rutile-TiO.sub.2. The TiCl.sub.4 can also be hydrolyzed and then calcined to yield the rutile-TiO.sub.2.
Applicants are also the inventors of related processes for the manufacture of synthetic rutiles from ilmenite as set forth in U.S. Pat. Nos. 3,252,787 and in U.S. Patent application Ser. No. 284,541 filed Aug. 29, 1972 now U.S. Pat. No. 3,929,962.
In the first of these, the iron content of the ilmenite is first oxidized and then reduced to metallic iron. The metallic iron is then leached from the TiO.sub.2 residues by solution in ferric chloride solution. As taught in that patent, in order for the reduction to metallic iron be readily accomplished, it is preferred to initially convert, by oxidation, the ferrous iron in the ilmenite to ferric iron prior oxidation step. It is required by that process that reduction be carried out at temperatures between about 750.degree. to 1250.degree. C and preferably about 900.degree. C.
The second invention, is based upon an improved yield with reduced magnesium impurities that results when small amounts of HF or fluorides are included in the hydrochloric acid solutions used to extract and dissolve the iron-free reduced ilmenite for the chloride process.
The processes described in these inventions are based upon integrated procedures utilizing high grade ilmenite or synthetic rutile as starting materials.